1. Field of the Invention
The present invention generally relates to a display panel, in particular, to an assembly method for display panel.
2. Description of Related Art
Liquid crystal on silicon panel (LCOS panel) is a liquid crystal display panel based on the silicon wafer backpanel. The LCOS panel using the silicon wafer as the backpanel utilizes the MOS transistor to replace the thin film transistor of conventional LCD device. The pixel electrode thereof mainly comprises metal material, and therefore the LCOS panel is a reflective liquid crystal panel. Because the metal pixel electrode of the LCOS panel completely covers a pixel region, especially the MOS transistor, therefore the image display quality of the LCOS panel is better than that of the conventional LCD device. Besides, the LCOS panel is based on the silicon wafer backpanel and has the advantages of compact volume and higher resolution. Therefore, the LCOS panel is broadly used in the liquid crystal projector, and it can meet the requirement of reduced volume.
FIG. 1 is a schematic cross-sectional view showing a conventional LCOS panel when assembling. Please refer to FIG. 1, when forming the LCOS panel, a silicon wafer backpanel and a glass substrate are assembled together, and then a cutting process is performed to form a plurality of LCOS panels. The structure of each LCOS panel is the same; therefore, only one LCOS panel is illustrated in the following for convenience.
A lower substrate 110 of the LCOS panel is a silicon substrate and an upper substrate 120 thereof is a glass substrate. When assembling the substrates, a sealant 130 is applied to the lower substrate 110. The material of the sealant 130 can be a UV curing resin for example. After that, the upper substrate 120 is aligned with the lower substrate 110, and then the two substrates are bonded together by a machine 30 under the atmosphere. Next, the sealant 130 is exposed to UV light in order to cure the sealant 130.
Generally speaking, the cell gap between the upper and lower substrates of the display panel is maintained by spacers, therefore, the amount and distribution of the spacers inside the display panel are related to the uniformity of the cell gap. However, the spacers are distributed inside the sealant 130. When the upper substrate 120 and the lower substrate 110 are bonded together by the machine 30, the stress is different between the region where the sealant 130 contacts with the two substrates, and other region where the sealant 130 doesn't contact with the two substrates. During the bonding process, the upper substrate 120 and the lower substrate 110 would be bended due to uneven stress. Therefore, the cell gap between the upper substrate 120 and the lower substrate 110 is not uniform, and Newton's ring would occur during display. This would affect the display quality of the LCOS panel severely.
Besides, the height of the spacer is about 2-3 μm in the LCOS panel. However, small particles having a diameter more than 3 μm would be easily generated under the atmosphere, therefore, the upper substrate 120 is not well bonded with the lower substrate 110. The phenomenon of Newton's ring becomes more severe.
FIGS. 2A and 2B are schematic views showing two kinds of protection resin coated on the silicon wafer backpanel. First, please refer to FIG. 2A, a wet process is performed when cutting the silicon wafer backpanel 50 and the glass substrate. In order to protect the silicon wafer backpanel 50 from being polluted by the liquid, a protection sealant 80 is coated on the silicon wafer backpanel 50 before it is assembled with the glass substrate. However, because the protection resin 80 is a protection frame of closed type, the air between the silicon wafer backpanel 50 and the glass substrate can not be removed, and therefore the desired cell gap can not be formed during the bonding process.
Please refer to FIG. 2B, a protection sealant 80 having a plurality of openings 82 is coated on the silicon wafer backpanel 50, and the openings 82 are sealed after the bonding process, in order to remove the air between the silicon wafer backpanel 50 and the glass substrate. However, this method requires an additional process of sealing the openings. Therefore, the fabrication time and cost are increased.